Manufacturers of microelectronic components often use thermocompression (TC) bonding to join external leads to film integrated circuits. TC bonds are known to be reliable provided the optimum parameters of time, temperature and pressure are used. The optimization of these parameters is obtained by analyzing the bond failure mode (e.g., lead failure, ceramic pullout) after destructive pull testing and adjusting the parameters accordingly. This process requires topographic examination, by conventional microscopy and/or scanning electron microscopy, of bonds which have been pulled to failure. Such detailed examination of the destroyed bond is subjective, time consuming, expensive and cannot be accomplished in real-time.
Stress Wave Emission (SWE) signals are a special class of sounds that have been used to detect ceramic microcracking as set forth in U.S. Pat. No. 3,924,456. SWE signals are transient elastic waves generated by the rapid release of strain energy from a localized source within a material. The SWE signal is characterized by a plurality of pulses having a low amplitude, short duration and a fast rise time.
U.S. Pat. No. 4,090,400 describes the non-destructive testing of a thermocompressively bonded beam lead device to determine the quality thereof by directing a short burst of air at the device and monitoring the bonds for SWE signals. The detected SWE signals are processed to determine the quality of the bond. Such a technique is most effective to measure bond quality, but if a bond failure occurs, there is no way to characterize the type of failure mode.
Accordingly, there exists a need for a real-time technique for determining the failure modes of bonds during destructive testing.